The present invention relates generally to fluid handling apparatus and, more particularly, to direct response valves of reciprocating type.
It is not uncommon for subterranean reservoir rocks to be fully saturated with oil and gas yet be of such low permeability that they are not feasible to develop in an economic manner. In such cases, production rates are often boosted by resorting to hydraulic fracturing, a technique that increases rock permeability by opening channels through which reservoir fluids can flow to recovery wells. During hydraulic fracturing, a fluid such as water is pumped into the earth under extremely high pressure where it enters a reservoir rock and fractures it. Sand grains, aluminum pellets, glass beads, or other proppants are carried in suspension by the fluid into the fractures. When the pressure is released at the surface, the fractures partially close on the proppants, leaving channels for oil and gas to flow to recovery wells.
Specialized pumps are used to develop the pressures necessary to complete a hydraulic fracturing procedure or xe2x80x9cfrac job.xe2x80x9d These pumps are usually provided with so-called fluid ends within which reciprocating plungers place fluids under pressure. Suction and discharge valves control fluid flow to and from the plungers. Improperly locating a valve in the fluid end at the time of manufacture can greatly weaken the fluid end, leading to a catastrophic pump failure. Similarly, a valve that has too many projections can capture or xe2x80x9cknock outxe2x80x9d enough proppant to block the flow of fluid through a pump requiring, at a minimum, that time and effort be invested to clear the blockagexe2x80x94a costly undertaking in an oilfield environment.
Commonly used discharge valves possess a plurality of guides or xe2x80x9cwingsxe2x80x9d that protrude into a valve seat to hold a piston in place. These wings are known to capture proppant from a fracture fluid under certain operating conditions. Such conditions should, however, be virtually nonexistent.
In light of the problems associated with fluid ends of pumps used for hydraulic fracturing, it is a principal object of the invention to provide a discharge valve that reduces the likelihood of proppant being knocked out of suspension to create a blockage. The discharge valve of the present invention, thus, offers few impediments (none whatsoever in a pumping chamber of a fluid end) to flow through a fluid end when open so that fracturing fluids can flow smoothly through it. As a result, fracturing fluids with higher than normal concentrations of suspended proppants can be pumped with substantial cost savings to the user.
It is an additional object of the invention to provide a discharge valve of the type described that, because of its compact size, can be positioned close to the suction valve that it may be paired with permitting faster transit times for a fluid through a pumping chamber and greater efficiencies in the operation of a pump.
It is another object of the invention to provide a discharge valve of the type described that can be seated in a relatively shallow pocket in a fluid end. As is well known, a valve pocket of shallow depth requires that less load-bearing material be removed from the body of a fluid end thereby enhancing the strength and durability of a fluid end. It is less likely, then, that a fluid end configured to receive the discharge valve of the present invention will fail from the development of excessive internal loads and stresses.
It is a further object of the invention to provide a discharge valve of the type described that utilizes a valve seat that abuts its supporting surface, i.e., a seat deck, at a shallow incline rather than at right angles as is common. A slope of about 30xc2x0 has been found to significantly reduce zones of stress transmitted through a fluid end. It is along such stress zones that fluid ends have been known to crack and fail under load.
Still another object of the invention is to provide a discharge valve of the type described that includes special porting to reduce the likelihood that the valve will become stuck in either an open position or a closed position during use. Therefore, the valve is virtually failsafe.
It is an object of the invention to provide improved elements and arrangements thereof in a discharge valve for the purposes described which is lightweight in construction, inexpensive to manufacture, and dependable in use.
Briefly, the discharge valve in accordance with this invention achieves the intended objects by featuring a valve seat and a piston with a bottom surface that is convex across its entirety for engaging the valve seat. The piston has a stem that extends upwardly from the head away from the valve seat and into a socket in a valve guide. The socket is formed in a conical prop projecting downwardly from a disc-like plug. A number of apertures traverse the plug and intersect the socket to providing pressure relief to the socket. A compressed spring is disposed between the valve guide and the head for normally retaining the head in engagement with the valve seat.
The foregoing and other objects, features and advantages of the present invention will become readily apparent upon further review of the following detailed description of the preferred embodiment as illustrated in the accompanying drawings.